In magneto-optic recording, data is represented as a magnetic domain in a magnetizable recording medium such as a disc. Each domain is a stable magnetizable data site representative of a data bit. Data is written to the medium by applying a focused beam of high intensity light in the presence of a magnetic field. The disc typically includes a substrate, a magneto-optic recording layer, a reflective layer, and two or more dielectric layers.
In substrate-incident recording, the beam passes through the substrate before it reaches the recording layer. The reflective layer in a substrate-incident recording medium is formed on a side of the recording layer opposite the substrate. The reflective layer reflects the beam back to the recording layer, increasing overall exposure and absorption.
In near-field, air-incident recording, the beam does not pass through the substrate. Instead, the beam is incident on the recording layer from a side of the disc opposite the substrate. In an air-incident recording medium, the reflective layer is formed adjacent the substrate. A solid immersion lens (SIL) can be used to transmit the beam across an extremely thin air gap, and through the top of the recording medium to the recording layer. The SIL can be integrated with a flying magnetic head assembly. The air gap forms a bearing over which the flying head rides during operation. For near-field recording, the thickness of the air gap is less than one wavelength of the recording laser beam. Transmission of a portion of the beam is accomplished by a technique known as evanescent coupling.
For either substrate-incident or air-incident recording, the recording beam heats a localized area of a recording medium having perpendicular anisotropy above its Curie temperature to form a magnetic domain. The area is allowed to cool in the presence of a magnetic field to orient the growing domain. The magnetic field is strong enough to overcome the demagnetizing field of the recording medium, causing the localized domain to acquire a particular magnetization. The direction of the magnetic field and the resulting magnetization determine the data represented at the domain.
With light intensity modulation (LIM) recording techniques, the magnetic field is maintained in a given direction for a period of time as the beam power is selectively modulated across the recording medium to achieve desired magnetizations at particular domains. According to magnetic field modulation (MFM) recording techniques, the beam is continuously scanned across the recording medium while the magnetic field is selectively modulated to achieve the desired magnetization. Alternatively, the beam can be pulsed at a high frequency in coordination with modulation of the magnetic field.
To read the recorded data, the drive applies a lower intensity, plane-polarized read beam to the recording medium. Upon transmission through and/or reflection from the recording medium, the plane-polarized read beam experiences a rotation in polarization. The angle of rotation varies as a function of the magnetization of the localized area. An optical detector receives the read beam and translates the rotation angle into an appropriate bit value.